Elevator systems typically include an elevator car positioned in a hoistway for carrying passengers and loads between various floors of a building. Elevator systems also include motors, which provide the requisite thrust force to move the elevator cars within the hoistways. Regenerative drives may be used to achieve desired elevator car movement and to generate electricity.
Regenerative drives may typically include a converter on the input or power utility grid side and an inverter on the motor side. In the design of the regenerative drive, power demand of the inverter is generally matched by an appropriate power capability of the converter on the input side. Power demands for operating elevators range from positive to negative. With positive power demands, externally generated power, such as power from a power utility grid, is used. With negative power demands, the load in the elevator drives the motor so it produces electricity as a generator. Use of the motor to produce electricity as a generator is sometimes referred to as regeneration. Regenerative drives may operate on a three-phase power input. In addition, regenerative drives may be multilevel with a multilevel converter and a multilevel inverter.
Management of acoustic noise, efficiency, neutral point stability and thermal balancing in the regenerative drive may be challenging. Accordingly, there exists a need for a control system and method that deliver beneficial results in acoustic noise, efficiency, neutral point stability and thermal balancing.